POS0873 SYNOVIAL TISSUE FEATURES ASSOCIATED WITH POOR PROGNOSIS IN INFLAMMATORY ARTHRITIS
Authors: A. B. Azuaga-Piñango, J. Ramirez, R. Celis, A. Cuervo, B. Frade-Sosa, J. C. Sarmiento-Monroy, J. A. Gómez-Puerta, R. Sanmartí, J. D. D. Cañete
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Rheumatoid arthritis (RA), Psoriatic arthritis (PsA), and undifferentiated arthritis (UA) are chronic immune-mediated inflammatory diseases characterized by joint inflammation. However, the prognosis related to progression to chronic and erosive disease or to an autolimited outcome could be different between those clinical phenotypes. Synovial lymphoid neogenesis (LN) has been previously studied as a prognostic factor in RA but results were conflicting between studies [1,2]. <h3>Objectives</h3> To evaluate the potential association of inflammatory cell infiltrates and the expression of ectopic LN structures in synovial tissue (ST) with poor prognosis factors (PPF) in patients with RA, PsA, and UA. <h3>Methods</h3> This is a retrospective study including patients with active RA, PsA, and UA who had ST obtained by rheumatological arthroscopy in our department. We evaluated clinical data and synovial LN and the cellular infiltrate by immunohistochemistry, as previously detailed [1]. Patients who were on Biologic Disease-modifying Antirheumatic Drug (bDMARDs) at the time of arthroscopy were excluded. PPF in patients with RA and UA were defined by anti-cyclic citrullinated peptide/protein antibodies (ACPA) and/or rheumatoid factor (RF), development of erosive disease or the initiation of bDMARDs during the follow-up. PPF in patients with PsA were defined by high levels of acute phase reactants (ESR and/or CRP), dactylitis or nail involvement at the time of arthroscopy and/or the initiation of bDMARDs. Statistical analysis was done with SPSS Statistics 27 program. For the analysis of LN and PPF, we performed x<sup>2</sup>, T-test to compare PPF with the cellular density and Spearman's rank correlation coefficient for cellular density and disease activity score 28 (DAS28). <h3>Results</h3> A total of 87 patients were included: 26 RA, 32 PsA and 29 UA. Demographic characteristics are detailed in Table 1. Seventeen out of 26 (65.38%) RA patients had LN and 14 (53.84%) had PPF. Twelve patients (46%) had LN and PPF. LN was associated with PPF (p 0.038). In PsA group, we found LN in 16 out of 32 (50%) and PPF in 42.4%. Polyarticular PsA (58.5%) was the most frequent phenotype and 15.2% of patients had onychopathy. Nevertheless, LN was not associated with PPF. Patients with PPF had a higher CD15+ polymorphonuclear cell density (477.63 [SD 410.68] vs 99.63 [SD 93.23] cells/cm2 in patients without PPF, p 0.031). Thirteen out of 29 (44.82%) UA patients had LN and 55.17% had PPF. The final diagnosis for these patients were: 12 RA; 4 PsA; 8 peripheral SpA and 5 remained as UA. LN was not associated with PPF. Synovial CD68+ macrophages cells density (lining, sublining and total) was negatively correlated with DAS28 CRP (r= -0.27, p 0.024). <h3>Conclusion</h3> Synovial LN was associated with PPF only in patients with RA, suggesting the specific pathogenic role that these well-compartmentalized lymphoid aggregated play in RA. However, in PsA, PPF was associated with synovial CD15+ neutrophils density, probably related to the pathogenic relevance of myeloid cells in this disease. Finally, synovial CD68+ macrophages negatively correlated with disease activity in UA patients, probably reflecting the heterogeneity of pathogenic mechanisms occurring in this group. Although this study is retrospective and with relatively small cohorts, the findings suggest a great heterogeneity of the ST features and its pathogenic implications in the subtypes of inflammatory arthritis studied. <h3>References</h3> [1]Cañete JD, Celis R, Moll C, et al. Ann Rheum Dis. 2009; 68(5):751-6. [2]Thurlings RM, Wijbrandts CA, Mebius R, et al. Arthritis Rheum. 2008;58(6):1582-9. <h3>Acknowledgements</h3> No acknowledgments to declare. <h3>Disclosure of Interests</h3> None Declared.